The background of the invention will be set forth in two parts.
1. Field of the Invention
This invention relates to microwave antennas and more particularly to circularly polarized microwave horn antennas used in antenna arrays.
2. Description of the Prior Art
In recent years there has been increased interest in microwave antenna systems and particularly in highly directional dual polarized microwave antenna arrays used in communication systems, for example. However, there is little known prior art designed for purification or reduction of axial ratio of circularly polarized horns which are arrayed in a multiple horn environment. It has been found that mutual coupling between the horns of an array significantly degrades the intrinsic polarization purity of the horns. As far as in known, existing techniques are generally applicable to a single polarization, i.e., fences, chokes, baffles, and the like, which are all polarization sensitive.
In contrast to the prior art, the invention utilizes the polarization characteristics of linear elements which act as coupling compensators between the horns of the antenna array and act as polarization trimmers to create very low cross polarization axial ratio, circularly polarized array patterns through a broad angular range.